A comparative study on geometries,stabilities, and electronic properties between bimetallic AgnX（X=Au,Cu;n=1-8）and pure silver clusters

Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geo- metric structures, the relative stabilities, and the electronic properties of bimetallic Ag n X (X=Au, Cu; n=1–8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n = 6 for the Ag n Au clusters, and at n = 5 for Ag n Cu clusters. For different-sized Ag n X clusters, one X (X=Au or Cu) atom substituted Ag n+1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps show interesting odd–even oscillation behaviours, indicating that Ag 2,4,6,8 and Ag 1,3,5,7 X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Ag n host to the impurity atom except for the Ag 2 Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd–even oscillations are found for the VIP and η of the Ag n X (X=Au, Cu; n=1–8) clusters.     

大尺寸MAPbI_3单晶的制备及光电性能研究

采用两步气相沉积法制备了大尺寸(150μm左右)高质量的MAPbI_3单晶,并通过对衬底表面修饰来调控晶体的成核位置.从衬底温度、载气流速、时间效应等方面系统探究了影响PbI_2晶体生长的因素.结果表明:该晶体生长的最优条件分别对应为350℃、20sccm、20min.将MAPbI_3单晶放置在空气中50天后,其X衍射特征峰没有明显变化.最后分析该器件的光电特性,发现其开关比高达10~4,响应度为3.8×10~4 A/W,且具有较快的响应速度(上升时间:0.03s;下降时间:0.15s).该MAPbI_3单晶光电探测器将在光电学领域有非常良好的应用.